The present invention relates to new uses of difluoromethoxy-2,2,2-trifluoroethane (E245) and of compositions which comprise a further solvent (cosolvent) in addition to difluoromethoxy-2,2,2-trifluoroethane. The invention furthermore relates to new compositions of E245 as a mixture with some of these solvents. A preferred use is a process for fixing toner applied to a recording material in the fixing device of a printer and/or copier by means of fixing vapor composed of E245. In this process, E245 may be used as such or as a mixture with a cosolvent.
In the printing and copying operation, a charge image (negative image) is produced initially on a photoconductor drum by exposure of the print or copy master to light and is developed in a subsequent developer station, i.e. the charge image is provided with toner. The developed charge images on the photoconductor drum then pass to a transfer station. An electrostatic field which exists in the transfer station draws the toner image over onto a record carrier, for example a web of paper or else an individual sheet, fed to the transfer station. The toner image now adheres to the surface of the record carrier, although it can be wiped off. The record carrier provided with the toner image (positive image) is then passed through a fixing device. A solvent vapor required for fixing the toner is generated in this fixing device. For this purpose, the solvent is located at the base of the housing of the fixing device. The base of the fixing device is heated by means of a heating device, so that the solvent vaporizes from the base. The resulting solvent vapor acts on the record carrier, and in particular on the toner applied thereto. In this process, so-called cold fixing, the solvent vapor thus ensures intimate contact between the toner and the recording material. The toner is thereby partially dissolved, so that it can penetrate into the record carrier. After this fixing operation, the record carriers are freed from any still adhering residues of the solvent vapor by drying, and a dry, firmly adhering toner image, which cannot be wiped off, is obtained on the record carrier.
Solvents for fixing the toner must meet particular requirements. Such solvents should have a relatively low boiling point and be non-flammable and essentially non-toxic, and should have favorable dissolving properties for, for example, toner particles which are applied to a recording material and are to be fixed by partial dissolving. As a rule, these requirements cannot be met by only a single solvent. A large number of solvent mixtures with more or less different compositions are therefore used in practice. It is therefore known in the prior art (for example in the field of industrial cleaning processes or in vapor degreasing), in addition to using pure chlorinated and/or fluorinated hydrocarbons, also to employ mixtures of chlorofluorohydrocarbons (as the primary solvent) with a cosolvent. Such mixtures can be either non-azeotropic or azeotropic or azeotrope-like. As used herein, the term "azeotrope-like" refers to mixtures which have an essentially constant boiling point (change in the boiling point by not more than 5.degree. C.) over a relatively wide mixing and concentration range. Such azeotrope-like mixtures therefore behave like azeotropes when used in practice. Those solvent mixtures which have a constant boiling point (maximum variation .+-.0.5.degree. C.) and which, on boiling, contain the solvent components of the mixture in the same relative composition in the vapor phase as in the liquid phase are referred to as azeotropes. Solvent mixtures which are suitable for use in fixing devices of printing and copying apparatus as a rule comprise at least two solvent components, at least one component of which must have the property of partially dissolving the toner. Since in modern fixing devices these solvent mixtures act on the toner in the vapor state, the most uniform possible vaporization of solvent mixtures, which are suitable in practice, is required, i.e. vaporization properties without separation into the components or at least without relatively large shifts in the ratios of the amounts of the components in the vapor phase relative to the liquid phase. The solvent mixture employed in the fixing device thus advantageously has at least azeotrope-like, but in particular azeotropic, boiling properties so that a constantly good fixing of the toner on the recording material can also be assured over relatively long periods of use.
The use of solvents in the fixing device of printing or copying apparatuses has already been described. For example, German Patent Application No. DE 2,835,284 -discloses azeotropic mixtures of trichlorotrifluoroethane (R113) and acetone. This specification also contains further details on the process of fixing the toner in a printing or copying operation.
Another process using partly halogenated chlorofluorohydrocarbons is described in WO 93/10485. In this process 2,2-dichloro-1,1,1-trifluoroethane (R123) and 1,1-dichloro-1-fluoroethane (R141b) are proposed as the primary solvent. Disadvantages include, however, that on the one hand the R123 proposed is not completely acceptable toxicologically under certain circumstances, and on the other hand R141b may be incompatible with other materials which may limit its use.
Although some efforts have already been made in the prior art to discover alternative compositions having the desired properties for various fields of use as substitutes for the completely halogenated hydrocarbons used heretofore, there remains a need for improvement on the basis of the use properties, toxicological properties and properties which affect the environment. For example, known solvent mixtures comprise relatively large amounts of solvents which in some cases are unacceptable toxicologically or environmentally or from a safety point of view (low flash point) . For a number of solvent constituents, substitution by other solvents which are at least equally suitable for the particular intended uses is desirable because of their properties which affect the environment.